The invention relates in particular, but not exclusively, to electromechanical camshaft adjusters and will be described in the following with reference to such an adjuster. However, the method proposed by the invention can also be used with other actuators such as, for instance, brush-type motors or electromagnets.
In an electromechanical camshaft adjuster known from WO 2004/035997 A1, the adjusting gear comprises a double eccentric gear and a double planetary gear. Through the use of such an adjusting gear with a high reduction gear ratio, it is possible to use a servomotor in the form of a compact, high-speed brushless DC motor comprising a high-induction permanent magnet. The servomotor can be integrated in the camshaft adjuster or be made as a separate component.
As a rule, electromechanical camshaft adjusters installed in motor vehicles are operated in a very wide temperature range from −40° C. to +120° C. ambient temperature. Under extreme conditions, as encountered in very hot areas or under particularly high engine loading, the ambient temperatures at the electromotor can reach values of up to 150° C., and the temperature can rise even higher due to the electric and mechanical power dissipation of the motor.
This demands suitable measures that prevent an overheating of the electromotor while simultaneously guaranteeing the full functionality of the adjusting device in as wide a temperature range as possible.
The object of the invention is therefore to provide an electromechanical adjusting device for the relative rotational angle adjustment of two shafts using a triple shaft gear which permits a reliable adjustment in a wider temperature range and which is capable of at least maintaining a set rotational angle when there is a danger of overheating of individual components. A further object of the invention is to propose a method for operating an actuator, particularly an adjusting device for adjusting the rotational angle in a triple shaft gear, which method must also guarantee operation in a wide temperature range with a high degree of operational reliability.